1. Field of the Invention
The present invention relates to a method for manufacturing an epitaxial wafer by forming an epitaxial layer on a surface of a semiconductor wafer such as a silicon wafer placed on a susceptor in a reaction chamber while rotating this wafer and to a holder configured to hold a wafer when forming an epitaxial layer on the wafer.
2. Description of the Related Art
There has been disclosed an epitaxial wafer manufacturing apparatus having a configuration in which at least a part of a lift pin is arranged on a lower side of a susceptor on which a wafer is mounted in an epitaxial layer forming chamber, this lift pin is inserted into a through bore provided in the susceptor to push up a wafer after forming an epitaxial layer, and heat transfer suppressing means suppresses heat transferred to a lift pin arrangement region via the lift pin at the time of forming the epitaxial layer between a wafer upper surface side and a susceptor lower surface side (see, e.g., Patent Document 1). This apparatus is configured in such a manner that a head portion of the lift pin is accommodated in the through bore of the susceptor and a leg portion protrudes toward a lower side of the susceptor. Further, in the heat transfer suppressing means, the lift pin is formed of a material having thermal conductivity that is less than 128 W/m·K lower than thermal conductivity of the susceptor. Furthermore, at least an upper surface side of the lift pin insertion through bore formed in the susceptor is tapered so that a bore cross-sectional area can be reduced from the upper surface side toward a lower surface side, and the head portion of the lift pin is formed into a dish-like shape so that the head portion can be fitted into the through bore without gap with an upper surface thereof being substantially conformed with an upper surface of the susceptor. It is to be noted that infrared lamps are arranged on an upper side and a lower side of the epitaxial layer forming chamber, and a wafer mounted on the susceptor is heated from both the upper and lower sides by these lamps. In the thus configured epitaxial wafer manufacturing apparatus, since the heat transfer suppressing means suppresses heat transfer from the upper surface side of the wafer toward the lower surface side of the susceptor via the lift pin during formation of the epitaxial layer, the heat transfer suppressing means can prevent a temperature in a region of the wafer facing the lift pin from becoming lower than a temperature of any other region. As a result, a reduction in depression of the epitaxial layer caused due to a decrease in temperature can be suppressed.    Patent Document 1    Japanese Unexamined Patent Application Publication No. 2000-323556 (claims 1 to 3, paragraph [0011], and paragraph [0025])
In the method for manufacturing an epitaxial wafer disclosed in Patent Document 1 according to the conventional technology, the lift pin is formed into a dish-like shape and the upper surface of the head portion of the lift pin is conformed with the upper surface of the susceptor so that the lift pin can be fitted into the through bore without gap. However, according to the manufacturing method disclosed in Patent Document 1, a difference in thermal conductivity is still produced due to a difference in shape or material between the susceptor and the lift pin, thermal release from the upper portion of the lift pin toward the lower portion of the same still occurs, and hence there arises a problem that a film thickness of the epitaxial layer at a position where the epitaxial layer faces the lift pin becomes uneven when an output ratio of the upper lamp and the lower lamp is changed.
On the other hand, since the susceptor that supports the wafer is present on the lower surface of this wafer, an output from the lower lamp is set to be larger than an output from the upper lamp so that the upper surface and the lower surface of the wafer can be uniformly heated. In this case, a temperature on a wafer back surface becomes lower than a temperature of the susceptor, and silicon is deposited on the wafer back surface, whereby there occurs a problem that the film thickness of the epitaxial layer at a position where the epitaxial layer faces the lift pin becomes uneven when lowering the output from the lower lamp is tried.